Grid probe structure



May 11, 1954 K. J. GERMESHAUS'EN GRID PROBE STRUCTURE Filed May 3, 1946INVENTOR KENNETH J. GERM ESHAUSEN ATTORN EY Patented May 11, 1954 GRIDPROBE STRUCTURE Kenneth J. Germeshausen, Newton Center, Mass., assignor,by mesne assignments, to the United States of America as represented bythe Secretary of the Navy Application May 3, 1946, Serial No. 666,880

4 Claims.

This invention relates in general to hydrogen thyratrons and moreparticularly to the prevention of grid emission in hydrogen thyratronsof the inside coated cathode type.

Thyratron tubes have many applications in electronic circuits. Hydrogenthyratrons have been developed having advantages over other thyratronswhich make them more desirable in many applications. A hydrogenthyratron is disclosed in patent application entitled HydrogenThyratron, Serial Number 576,113, filed February 3, 1945 by Kenneth J.Germeshausen. Grid emission, caused by cathode coating materials beingevaporated from the cathode and depositedon the grid has provedtroublesome in these tubes.

It is therefore anobject of this invention to prevent grid emission inhydrogen thyratron tubes employing inside coated cathodes.

It a further object of this invention to provide a tube structure whichmaintains good grid starting characteristics while preventing such gridemission.

These and other objects will be apparent from the followingspecification when taken with the accompanying drawing in which:

Fig. 1 illustrates the structure of this invention; and

Fig. 2 shows an improved type heater for oxide cathodes of the type usedin some thyratron tubes.

The invention will now be described in detail with reference to Fig. 1,which shows the electrode structure of a hydrogen filled thyratron typetube. For simplicity the envelope II has been symbolically shown. Anoxide film I is coated on the inside surface and enclosed by acylindrical conductive structure 12 which has an aperture I4 at the topas shown. The electron discharge from oxide film l0 passes through thisorifice toward the grid and anode. A cylindrical grid structure I6 isplaced around cylindrical structure l2. This grid has a transverse meshis between the top of cylindrical structure I2 and anode 20.

' To prevent grid emission, it is necessary to keep evaporated metal,such as barium, from the oxide film l0 away from mesh section I8 of thegrid structure. This is accomplished by placing a baflle 22 between thecathode, structure [2 and grid mesh I8. This battle is conductivelyattached to the cathode structure [2 by a supporting member 24. Thebafiie when connected in such a manner shields the grid 18 and preventssubstantially all evaporated metal from reaching the grid mesh 18.Bafile 22 connected in this manner shields the cathode so completelythat it is difi'icult to start a discharge between grid and cathode tostart thyratron conduction. To eliminate this diificulty and increasecontrol sensitivity a small diameter probe 26 is attached to grid mesh18 and extends axially through a small aperture in the center of baflie22 a short distance in the direction of cathode structure I2. This probe26 enables the start of a discharge between grid mesh [8 and cathode [2,which readily reaches the anode. The small area of the probe 26 exposedto the cathode discharge, its location, and small cross-section preventit from causing grid emission difficulties even through some evaporatedmetal may be deposited on the end of the probe.

Thus it may be seen that this invention provides means for preventinggrid emission trouble in hydrogen thyratrons of inside coated cathodetypes without interfering with the desirable operating features of suchtubes.

Now referring to Fig. 2 there is shown an improved type heater for usewith oxide cathodes. A cathode 40 with an electron emissive coating 42is heated by a heater element 44 inside the cathode sleeve 40. Theheater element 44 is constructed of a ribbon shaped metal such astungsten. The cross section of the ribbon is selected such that adjacentturns of the helically wound ribbon touch each other and completely fillthe space inside the cathode sleeve 40. As the heater 44 is operated atlow voltage, no special insulation is required. This constructionprevents sagging of the heater, and it is thus possible to use ribbon ofless refractory metal than tungsten, as for example, molybdenum. Inaddition to these features, the arrangement shown, wherein adjacentturnsare in contact presents almost a uniform heating surface to providevery uniform heating of the cathode sleeve 40 and coating 42.

It is believed that the construction and operation as well as theadvantages of my improved thyratron tube structure will be apparent fromthe foregoing detailed description thereof. It

will also be apparent that while I have shown and described myinvention, in a preferred form, changes may be made in the apparatusdisclosed without departing from the spirit of the invention as soughtto be defined in the following claims.

What is claimed is:

1. A hydrogen thyratron having an anode, a cylindrical cathode and acylindrical sleeve mesh and connected electrically to said cathode forpreventing grid emission in said tube, and a 7 probe connected to saidgrid and extending through said baflle plate aperture toward saidcathode.

2. A hydrogen thyratron having an anode, a cylindrical cathode and acylindrical sleeve shaped grid, said cylindrical cathode having aninside coating and an aperture at one end thereof for the emission ofelectrons toward said anode, said grid substantially enveloping saidanode and said cathode and having a transverse wire mesh secured theretobetween said anode and said cathode, a transverse bafiie plate betweensaid cathode and said grid having a small central aperture and connectedto said cathode for preventing grid emission in said tube, and a shortprobe connected to said grid and extending axially a short distancethrough said aperture toward said cathode for providing sensitiveconduction control.

3. A hydrogen thyratron having an anode, a cylindrical cathode and acylindrical sleeve shaped grid, said cylindrical cathode having aninside coating and an aperture'at one end thereof for the emission ofelectrons toward said anode, said grid substantially enveloping saidanode and said cathode and having a transverse wire mesh secured theretobetween said anode and said cathode, a baifie having a centrally locatedaperture between said grid and said cathode for preventing substantiallyall metallic particles evaporated from said cathode from reaching saidgrid, and a short probe fastened to said grid and extending axiallythrough said aperture a short distance toward said cathode, said baffleand probe being operative to provide accurate conduction control by saidgrid with substantially no grid emission.

4. An electron tube having at least a cathode, an anode and a grid, saidcathode being substantially a hollow cylinder open at one end and coatedon the interior surfaces thereof with electron einissive material, saidgrid being a hollow cylinder concentric with and substantiallysurrounding said cathode and said anode, a circular mesh affixed withinsaid grid cylinder transversely thereof and disposed between saidcathode and said anode, a. probe extending from said mesh toward saidcathode, an annular baffie plate disposed between said cathode and saidmesh and conductively connected to said cathode, said annular baflleplate surrounding said probe.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,893,837 Giard Jan. 10, 1933 2,014,539 Stansbury Sept. 17,1935 2,032,179 Lowry Feb. 25, 1936 2,065,997 Edwards Dec. 29, 19362,106,847 Kniepkamp Feb. 1, 1938 2,166,817 Maser July 18, 1939 2,271,938Etzrodt Feb. 3, 1942 2,273,054 Le Van Feb. 17, 1942 2,392,397 LittonJan. 8, 1946 2,399,003 Crapuchettes Apr. 23, 1946 2,416,661 Lawton Feb.25, 1947 2,492,665 Sloan Dec. 27, 1949 2,492,666 Sloan Dec. 27, 19492,572,881 Rothstein Oct. 30, 1951

